Prior art workers have devised and suggested a variety of mechanisms for modifying the simple pivotal movement of the tool during the cutting operation in order to form the desired aspherical surfaces. However, these prior art devices involve the use of cams, patterns and other linkages and mechanisms which may result in the translation of a portion of the tool carriage during the cutting operation.
Examples of such prior art devices are shown in the following U.S. Pat. Nos.: 4,051,751; 3,835,588; 3,977,279; 3,835,588; and 913,274.
The difficulty with such prior art devices is that mechanical parts which will move in linear translation relative to each other, such as a sliding or translating table, cannot be machined to the close tolerances to which rotating or pivotal parts can be machined. Such sliding tables are also subject to considerable wear. Therefore, the translation movement is done with parts which interfit in a relatively sloppy manner. The resulting lense surface is not cut sufficiently smoothly and accurately.
Additional lense shaping apparatus is shown in these following U.S. Pat. Nos.: 2,880,556; 3,662,040, 3,117,396; 2,545,447, 3,763,597; 2,633,675, 3,015,196; 3,289,355; 596,503; 3,913,274; 2,806,327; 2,403,668; 2,427,020; 3,468,067; 2,556,604; 2,237,744; and 3,853,499.
If a cam or pattern and a cooperating cam follower are used, they require a spring. The spring will change its applied force as it is used so that the cam follower will be a different distance from the cam after the spring force changes.